Just in reviewing the iFixIt guides for the current MacBook Pro's Retina & Non-Retina theres enough differences mechanically that you can't just swap the display assembles as the Non-Retina MBP has it's the antenna connections at the hinge while the Retina version has the camera & antenna connections across the fan to the logic board. The video connectors are not the same type so you have some issues there.
Given the fact the connector is the same size on the logic board the number of execution units needs to be able to support the display which the two GPU's don't have (12 Vs 16). 3000 4000
Even if you were able to make things fit the MBP GPU limitations can't drive the Retina display properly (As MacHead & Marcel describe above). The lack of VRAM also means you can't drive all of the displays pixels discretely. Instead you'll get a quad of pixel cells if the video driver is able to scale, I doubt it will so you'll get a 1/4 image as the driver thinks it can light each discreet pixel so 3/4 of the display will be dark. It's similar to what happens when you select a smaller setting in the Display Pref. But, unlike the pref setting which will center the image it will take the top left part of the display area.
I encountered a similar type of issue when higher res VGA displays came out.